The yield of the tokens still makes it a no brainer buy for some, you only have to believe the site will continue as it has done previously and also to have a use for the site to have a natural interest in holding those tokens. The yield will repay what you put in, this will vary in the timeframe by the amounts gambled and also held on deposit. The spins is a side bet, a bonus to keep you entertained while waiting for the full year to mature etc.
It adds up ok for some but not all of course, most of the users of the site are probably just random public and not holding that much BTC which is normal so the spins matters alot to the average masses and its a big fail not to deliver for those very vocal masses surely.
As FUN lost price, they should have balanced the premium tiers costs accordingly, just like they do with faucet hourly rewards and WoF rewards.
Sounds like a fair idea but I'd guess its a balance sheet entry for them as a token total mass or market capitalization. BTC altering the outcome of each spin adds stability in the result cost, for a business anything that adds stability is a big plus. I would guess they already consider the lock and pay for doing that as the benefit to long term holders and in proportion to the amount held. Iam wondering if the token movements are as mysterious and long term as BTC itself, hopefully we find out this is just a 2016 moment.